Nylon barrier board structure

ABSTRACT

A paperboard laminate useful for making gable top juice cartons is provided. The laminate provides for a high melting point polymer such as a semi-crystalline nylon to be applied directly to a board surface as an oxygen barrier layer. An anti-scalping layer is also provided by a polar polymer which is connected by a tie layer to an outermost skin coat layer. Positioned between the skin coat layer and the oxygen barrier layer are one or more bulk layers of polyolefins. The resulting laminate affords a juice carton which has good oxygen barrier and Vitamin C retention properties, is resistant to overactivation during heat sealing, has minimal scalping of d-limonene and essential oils, and has excellent bulge resistance.

RELATED APPLICATIONS

This application claims the benefit of U.S. application Ser. No.10/431,955 filed on May 8, 2003, and PCT Application PCT/US2004/014305filed on May 7, 2004, both of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention is directed towards a paperboard laminate usefulfor making containers for citrus juices and beverages, as well as driedfood products. In addition, the paperboard laminate is useful for makingcontainers for liquid non-food products such as fabric softeners. Thepresent invention uses two layers of Nylon 6 separated by a low densitypolyethylene layer to provide a resulting laminated structure havinggood oxygen barrier properties, abuse resistance, and protection ofproducts packaged therein against the loss of vitamins, flavor, andessential oils. The innermost layer of Nylon 6 is applied directly tothe board substrate and provides an oxygen barrier which also protectsagainst overactivation of the board. An additional layer of Nylon 6provides an anti-scalping layer and is placed adjacent the skin coatlayer. The skin coat layer and the adjacent Nylon 6 layer are joined byan adhesive tie layer. The resulting laminate provides for a boardstructure and carton which are resistant to the creation of pin holes inthe laminated layers which may occur through overactivation of theboard. Further, the resulting cartons have excellent resistance toscalping. The resulting laminate structure also provides for anassembled carton which, when filled with an aqueous liquid, has goodresistance to carton bulge over the life of the carton.

BACKGROUND OF THE INVENTION

This invention relates to coated paperboard which may be used within thebeverage industry to provide containers for citrus and fruit juices,milk, and other liquid and non-liquid food products. A variety ofcoating layers are known to be used to provide useful properties to theresulting paperboard laminate. For instance, within the citrus juiceindustry paperboard cartons have coatings designed to provide an oxygenbarrier. The incorporation of oxygen barriers into a laminate structurehelps preserve Vitamin C content against oxidative loss and contributesto a longer product shelf life.

In addition, juice cartons are prone to scalping of essential oils inthe carton's contents by the skin or product contact layer of thelaminated board. As such, barrier coatings which provide increasedresistance to scalping are also desirable.

Extruded nylon has been used as one layer of a multi-component laminatedstructure for a barrier board. One such barrier board which provides foroxygen barrier properties and reduces essential oil loss is disclosed inThompson et al, U.S. Pat. No. 4,777,088.

Brown et al, U.S. Pat. No. 4,753,832, also discloses a nylon oxygenbarrier layer as part of a laminated structure. The Brown et al layerprovides a skin layer of glycol-modified polyethylene terephathalate(PET-G).

Parks et al, U.S. Pat. No. 6,149,993, discloses a layer of amorphousnylon as an oxygen barrier structure. Amorphous nylon has relatively lowstrength as compared to Nylon-6 and other semi-crystalline nylonstructures. The Park et al reference proposes that the oxygen barrierproperties of amorphous nylon are equivalent to the barrier propertiesof laminated structures containing ethylene vinyl alcohol (EVOH).

An EVOH barrier laminated structure may be seen in reference to theGibbons et al, U.S. Pat. No. 4,701,360, in which EVOH is provided as aheat-sealable oxygen barrier that offers resistance to scalping whenpresent as the skin layer of a board laminate.

While the art provides for a variety of laminated barriers for cartons,there remains for room for variation and improvement within the art.

SUMMARY OF THE INVENTION

It is one aspect of at least one of the present embodiments of theinvention to provide an improved, heat-sealable laminated boardstructure for a juice carton which exhibits excellent oxygen barrierproperties. The oxygen barrier properties provide for the retention ofhigh Vitamin C levels. Juice cartons constructed from the laminate boardstructure also offer good resistance to scalping of essential oils.

It is yet another object of at least one of the present embodiments toprovide a heat-sealable paperboard laminated structure which may be usedfor fruit or citrus juices, other beverages, dry food products, andnon-food liquid products such as fabric softeners. The multi-layerlaminated structure contains two distinct, separated layers of a highmelting temperature polyamide such as Nylon 6 applied to the productside of a paperboard substrate. The innermost layer of Nylon 6 providesan oxygen barrier which is resistant to overactivation.

The outermost layer of Nylon 6 provides a barrier against scalping ofessential oils which further protects the extruded, laminated layersduring heat sealing steps associated with the folding and filling ofcartons.

It is yet another aspect of at least one of the present embodiments ofthe invention to provide a laminated board structure in which theextruded polymer layer prevents blistering and pinholing of thelaminated layers (overactivation) during heat sealing of the cartons. Inaccordance with this invention, it has been found that when a carton isheat sealed, the paperboard substrate is often raised to a temperaturein excess of the boiling point of water. As such, moisture in thepaperboard layer turns to steam, the release of which may compromise thestructural integrity of the various laminated layers (boardoveractivation). The damaged lamination layers provide undesirablepathways through the laminated structure for oxygen and moisture.Several of the embodiments described herein provide for laminatedstructures which are resistant to overactivation.

Thus, in one embodiment of the present invention a paperboard, coatedwith an outer heat-sealable polyolefin layer, is provided as a coatedbase substrate upon which an inner, laminated structure is extruded. Theextruded, laminated structure, from the exterior (gloss side) of thelaminated structure to the interior of the structure, comprises thefollowing layers:

-   -   polyolefin/paperboard/Nylon 6/tie layer/polyolefin/tie        layer/Nylon 6/tie layer/polyolefin.

It is yet another embodiment of at least one of the present inventionsto provide a laminated structure for paperboard cartons in which anouter skin layer of a polyolefin or other heat-sealable material isattached to an anti-scalping layer such as Nylon 6, Nylon 6/6, amorphousnylon, or other polar polymer material using an adhesive tie layer. Theanti-scalping layer, when a high melting polar polymer is used, alsoprovides additional protection to the paperboard against overactivation.

Cartons can be constructed from the laminates of the present inventionwhich provide excellent gas-barrier protection for food and non-foodproducts. Further, the resulting carton has been found to offer asignificant reduction in scalping of essential oils which furtherextends the shelf life and quality of a juice product.

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A fully and enabling disclosure of the present invention, including thebest mode thereof, to one of ordinary skill in the art is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying drawings.

FIG. 1 is a schematic cross-section illustrating a barrier boardlaminate according to the present invention;

FIG. 2 is a graphical representation of Vitamin C retention in a cartonconstructed from a laminate in accordance with the present invention;

FIG. 3 is a graph of d-limonene levels of orange juice in cartonsaccording to the present invention; and,

FIGS. 4A and 4B are graphical representations of the respective bulgeand normalized bulge properties of cartons according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference now will be made in detail to the embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncover such modifications and variations as come within the scope of theappended claims and their equivalents. Other objects, features, andaspects of the present invention are disclosed in the following detaileddescription. It is to be understood by one of ordinary skill in the artthat the present discussion is a description of exemplary embodimentsonly and is not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstructions.

In describing the various figures herein, the same reference numbers areused throughout to describe the same material, apparatus or processpathway. To avoid redundancy, detailed descriptions of much of theapparatus once described in relation to a figure is not repeated in thedescriptions of subsequent figures, although such apparatus or processis labeled with the same reference numbers.

An embodiment of the present invention may be provided by a paperboardlaminate having the structure as seen in reference to FIG. 1. When thestructure is assembled into a carton, the structure has been found toprovide excellent oxygen barrier properties, good resistance to bulge,resistance to oxidative loss of Vitamin C, and provides a skin coatlayer which minimizes the uptake of essential oils such as d-limonene.

The laminated structure 1, as seen in reference to FIG. 1, may beprovided by a conventional paperboard substrate. The substrate usedherein is a 23 point paperboard 10 having a basis weight of 280lbs/ream. A gloss or exterior surface 12 of the paperboard 10 may beprovided as a 16 lb/ream weight coating of low density polyethylene(LDPE) applied following conventional flame treatment of the paperboardsubstrate. Subsequent corona treatment, as is conventional within theart, is used to achieve a surface energy of about 42 to about 43 dynswhich facilitates printability of the gloss layer(s).

As seen in FIG. 1, an interior surface of the board has extrudedthereon, in sequence from the board to the outermost product contactlayer, a 5 lb. layer of Nylon 6 (layer 14); a 5 lb. layer of an adhesivetie layer (layer 16); a 20 lb. layer of LDPE (layer 18); a 3 lb. layerof an adhesive tie layer (layer 20); a 3 lb. layer of Nylon 6 (layer22); a 3 lb. layer of an adhesive tie (layer 24); and, a skin coat layerof 3 lb. of LDPE (layer 26). In all examples set forth herein, thecoating weights are per 3,000 sq. ft. of board surface.

The LDPE used on the gloss 12 and skin coat layer 26 is a Chevron 4517LDPE which may be extruded onto the board at a temperature of about 600°F. The possible operative extrusion temperatures of LDPE are well knownto one having ordinary skill in the art and may be varied within theknown acceptable temperature ranges. The Nylon 6 is a B85QP (Honeywell)material extruded at 580° F., though a lower extrusion temperature ofabout 500° F. is recommended. The respective tie layers are low densitypolyethylene Plexar® 175 (Quantum Corp.) and may be extruded at atemperature of about 600° F.

The resulting laminate may be scored and cut into blanks which may besubsequently folded. The side seams may be heat sealed as isconventional within the art. The prepared blanks are then ready to befilled with juice or other product and sealed using conventionalequipment and techniques.

While the structure seen in reference to FIG. 1 and described in moredetail above is given in reference to specific polymers and tie layers,a variety of different polymers may be used in accordance with the scopeof the present invention. For instance, suitable heat-sealablepolyolefins may include polypropylene, high density polyethylene, mediumdensity polyethylene, low density polyethylene, linear low densitypolyethylene, and combinations thereof. Various additives may beincluded in the polyolefins so as to achieve desired extrusion,adhesion, or heat sealing properties. Coating weights for the gloss sideof the board may be between about 6 to about 20 lbs/ream. The skin coatweights of the polyolefins may vary between about 2 to about 28lbs/ream. However, as noted below, a skin coat layer selected from thelower end of the coating ranges is preferred so as to minimize scalpingof essential oils.

Positioned between the oxygen barrier layer 14 and the anti-scalpinglayer 20 is a relatively thick 20 lb. layer of LDPE (layer 18). Theinclusion of a relatively thick layer of LDPE within the laminatedstructure has been found useful in that the added bulk material furtherminimizes the overactivation of board during heat sealing. Additionally,the LDPE layer 18 also limits water vapor loss of carton contents whichis particularly important for non-refrigerated liquids such as fabricsofteners which must have extended shelf lives in low humidity storageenvironments. The bulk and density of the LDPE helps insulate the boardsubstrate during heat sealing operations and provides for a more rigidcarton which resists bulge. While a 20 lb. coating weight is used in theexample set forth below, the coating weight of the LDPE may range frombetween about 10 to about 24 lbs/ream. Additionally, the variouspolyolefins described above may also be used in place of the low densitypolyethylene within layer 18. Likewise, similar properties may beachieved by using multiple layers of polyolefin, along with anynecessary adhesive tie layers, so as to achieve the similar benefits andattributes of the bulk polyolefin layer 18.

Paperboards suitable for use with the present invention may include arange of paperboard stock having a basis weight of between about 150 toabout 300 lbs/ream.

The oxygen barrier layer 14, represented in FIG. 1 by the 5 lb. Nylon 6layer, may include other extrudable polymers including othersemi-crystalline nylons or semi-crystalline polyamides such as Nylon4/6, Nylon 6/6, Nylon 6/12, Nylon 11, and Nylon 12, aromatic containingpolyamides, as well as Amorphous Nylon, EVOH, blends of AmorphousNylon/EVOH, PET, PET-G, other polyesters and combinations thereof. Theoxygen barrier layer may be present in a coating weight of between about3 to about 16 lbs/ream, the coating weight varying depending upon theactual oxygen barrier material selected. It is well within the skilllevel of one having ordinary skill in the art to select and apply anappropriate amount of an oxygen barrier material by conducting routinetests to determine the effectiveness of the oxygen barrier. The highmelting point oxygen barriers such as the semi-crystalline nylons orsemi-crystalline polyesters are believed most useful in minimizingoveractivation of the board during heat sealing operations and arepreferably applied directly to a surface of the board.

The tie resins suitable for co-extrusion with the individual laminatedlayers may include a variety of conventional tie resins such asanhydride modified co-polymers available under the trade name of Bynel®(DuPont Corp.) along with the Plexar® resins noted above. Useful coatinglevels of tie layers include about 2 to about 6 lbs/ream coating weight.

The anti-scalping layer, represented in FIG. 1 by the 3 lb. layer ofNylon-6, may include other extrudable barrier layers or films. In atleast one embodiment of the present invention, it is useful if theanti-scalping layer is selected from a polar polymer or film having ahigh melting point. The high melting point further minimizes transfer ofheat from the skin coat side of the laminate to the underlying boardsubstrate, thereby minimizing overactivation of the board and theresulting pin holes or blistering of the oxygen barrier layers andlaminated layers which results from evolved steam. As such, theintegrity of the oxygen barrier layer(s) is maintained.

Amorphous nylon may also be used as the anti-scalping layer 22.Amorphous nylon provides excellent oxygen barrier properties to theoverall structure and works well in high humidity environments such asthose encountered in refrigerated juice cartons.

As set forth in the examples which follow, a structure as seen in FIG. 1(N6C) and comparative structures were evaluated with respect to VitaminC retention, d-limonene uptake (scalping), and carton bulge. Thecomparative structures included quart size glass containers (glass).Additionally, a commercially available control structure having thedesignation VS+10 was also evaluated. The VS+10 structure is as follows:

-   -   16# LDPE/23 point 280#board/5#Nylon-6/5#Plexar® 175 tie        layer/26# LDPE

Example 1

A laminate according to the embodiment seen in reference to FIG. 1 wasprepared and converted into carton blanks as previously described. Thecarton blanks were filled with orange juice under refrigeratedconditions and stored at 5° C. for 49 days. Vitamin C levels weredetermined on the intervals as seen in reference to FIG. 2, usingestablished protocols of starch-iodine titration. Comparison tests fromthe glass and VS+10 containers were also conducted. The results, setforth in FIG. 2, indicate that the N6C laminate has Vitamin C retentionproperties better than the VS+10 comparative structure. The Vitamin Cdata indicates that the laminate constructed according to one aspect ofthe present invention provides an effective oxygen barrier as reflectedby the improved Vitamin C levels. Oxidative loss of Vitamin C withinpaperboard cartons is correlated with oxygen transmission rates throughthe laminated structure, along with dissolved oxygen and head spaceoxygen. The improvements in oxygen transmission are believedattributable to the integrity of the oxygen barrier layers and otherlaminate layers which are present during the heat sealing steps.

As seen in reference to FIG. 3, the laminate of the present inventionalso provides significant improvements with respect to scalping ofd-limonene, an essential oil. The measurements of d-limonene are setforth as percent volume in FIG. 3 and were derived using the Scottmethod for percent oil. As indicated in the data in FIG. 3, thed-limonene loss is greatly improved compared to the control VS+10structure. The improvements in d-limonene loss are attributable to theanti-scalping barrier of Nylon 6 material which is secured to the skincoat layer by a tie layer. The polar nature of the anti-scalping barrierlimits the uptake of d-limonene to the relatively thin skin coat layer26 and adhesive tie layer 24. Further, d-limonene loss comparesfavorably to the glass container indicating only a minimal amount ofd-limonene loss attributable to scalping. As reflected by the data inFIG. 3, the majority of d-limonene loss occurs immediately followingfilling and d-limonene levels are substantially stable thereafter. Tothe extent an anti-scalping barrier such as Nylon-6 is used which alsohas oxygen barrier properties, the overall oxygen barrier properties ofthe resulting laminate are also enhanced.

As seen in reference to the data set forth in FIGS. 4A and 4B, bulgedata for the control VS+10 structure and the N6C structure of thepresent invention were measured and plotted. As seen, the N6C carton ismore resistant to bulge than the control VS+10 structure. Carton bulge,as described in Applicant's commonly assigned U.S. Pat. No. 6,372,317,and which is incorporated herein by reference in its entirety and forall purposes, may be controlled by reducing the rate of moisturetransmission through the carton board. Without being limited by theory,it is believed that the improvements in carton bulge are attributable inpart to the improved integrity of the laminated layers which form thecarton. The ability of the resulting board structure to avoidoveractivation preserves the structural and functional integrity of thelaminated layers. Improved integrity minimizes both oxygen transmissionrates and water vapor transmission rates. The reduction in watertransmission rates is believed to correlate with the noted improvementsseen in carton bulge.

Additionally, the use of a high semi-crystalline nylon as discussed insome embodiments as oxygen barrier layers and/or an anti-scalping layer,imparts additional stiffness to the laminated structure which alsocontributes to the overall bulge resistance of the carton.

As set forth in Applicant's co-pending application having Ser. No.60/428,293, entitled Improved Flavor Barrier, and which is incorporatedherein by reference in its entirety, calcium carbonate and other organicand inorganic fillers described may be incorporated into skin coat 26and tie layer 24 at a percent by weight loading of at least about 10 to20 percent. The inclusion of a filler into the skin coat and tie layerresins will further reduce the amount of d-limonene which is scalped bythe polyolefin polymers.

Although preferred embodiments of the invention have been describedusing specific terms, devices, and methods, such description is forillustrative purposes only. The words used are words of descriptionrather than of limitation. It is to be understood that changes andvariations may be made by those of ordinary skill in the art withoutdeparting from the spirit or the scope of the present invention, whichis set forth in the following claims. In addition, it should beunderstood that aspects of the various embodiments may be interchanged,both in whole or in part. Therefore, the spirit and scope of theappended claims should not be limited to the description of thepreferred versions contained therein.

1. A laminate structure comprising: a paperboard substrate having aninner surface and an outer surface; a layer of a heat-sealable polymercoated on the outer surface of the paperboard substrate; asemi-crystalline polyamide polymer layer coated on the inner surface ofthe paperboard substrate; a first tie layer coated on an inner surfaceof the semi-crystalline polyamide polymer layer; at least one layer ofpolyolefin polymer coated on an inner surface of the first tie layer; asecond tie layer positioned on an inner surface of the at least onelayer of polyolefin polymer; a polar polymer scalping barrier layerselected from the group consisting of a semi-crystalline nylon, anamorphous nylon, a polyester, and combinations thereof on an innersurface of the second tie layer; a third tie layer positioned on aninner surface of the polar polymer scalping barrier layer; and, aheat-sealable polymer layer coated on an inner surface of the third tielayer.
 2. The laminate structure according to claim 1 wherein saidsemi-crystalline polyamide polymer layer further comprises a nylonselected from the group consisting of Nylon 4/6, Nylon 6/6, Nylon 6/12,Nylon 11, Nylon 12, and combinations thereof.
 3. The laminate structureaccording to claim 1 wherein the polar polymer scalping barrier layer isa high melting point semi-crystalline polyamide.
 4. The laminatestructure according to claim 2 wherein said polar polymer scalpingbarrier layer comprises a high melting point semi-crystalline polyamide.5. The laminate structure according to claim 1 wherein saidsemi-crystalline polyamide polymer layer and said polar polymer scalpingbarrier layer are Nylon
 6. 6. The laminate structure according to claim1 wherein said semi-crystalline polyamide polymer layer and said polarpolymer scalping barrier layer is Nylon 6/6.
 7. The laminate structureaccording to claim 1 wherein said at least one layer of polyolefinpolymer on an inner surface of the first tie layer has a coating weightof about 12 to about 24 lbs/3,000 sq. ft.
 8. A laminate structureconsisting essentially of: a paperboard substrate having an innersurface and an outer surface; a layer of a heat-sealable polymer coatedon the outer surface of the paperboard substrate; a semi-crystallinepolyamide polymer layer coated on the inner surface of the paperboardsubstrate; a first tie layer coated on an inner surface of thesemi-crystalline polyamide polymer layer; at least one layer ofpolyolefin polymer coated on an inner surface of the first tie layer; asecond tie layer positioned on an inner surface of the at least onelayer of polyolefin polymer; a polar polymer scalping barrier layerselected from the group consisting of a semi-crystalline nylon, anamorphous nylon, a polyester, and combinations thereof on an innersurface of the second tie layer; a third tie layer positioned on aninner surface of the polar polymer scalping barrier layer; and, aheat-sealable polymer layer coated on an inner surface of the third tielayer.